Control mechanisms for an optical objective having a zoom control element



2 Sheets-Sheet 1 DErreR R. PLUMMER Sept 3, 1968 n. R. PLUMMER CONTROL MECHANISMS FOR AN OPTICAL OBJECTIVE HAVING A ZOOM CONTROL ELEMENT Original Filed Jan. 16, 1964 Sept 3, 1968 n. R. PLUMMER 3,400,212

CONTROL MECHANISMS FOR AN OPTICAL OBJECTIVE HAVING A ZOOM CONTROL ELEMENT Original Filed Jan. 16, 1964 2 Sheets-Sheet 2 LJ# fjrvph'jfz'ej Inventor DE XTEKR R. PLUMMER B MWL?. WMA* Attorneys Unit-edl *States Patent i CONTROL MECHANISMS FOR AN OPTICAL..

' OBJECTIVE HAVING A ZOOM` CONTROL ELEMENT Dexter R. Plummer, Leicester, England, assignor to Rank Precision Industries Limited, trading as The Rank'Organisation Rank Taylor Hobson Division, Leicester,

England, a British company Continuation of .application Ser. No. 338,073, Jan. 16,

1964. This application Aug. 28,1967, Ser. No. 663,902 1 Claims priority, application Great Britain, Jan. 18, 1963,

4Y Claims. (Cl. 178-7.92)

Control mechanism for an optical objective of the zoom type comprising means for effecting movement of:amovlable optical member of said-system in accordance with the movement of a first control element, said mechanism comprising an electrically energized prime mover .for driving said movable member and having an output drive whose speed is dependent on a controlling voltage input to such prime mover, a tachogenerator having an output voltage approximately proportional to the-speed at which it is driven, a transmission mechanism interposed between said first control element and such tachogenerator whereby the tachogenerator is driven at a speed greater than and approximately proportional to the speed of movement of said first control element, amplifying means whose output constitutes the said controlling voltage input to the prime mover, means for supplying an input tothe amplifying mean-s which is dependent on the output voltage of the tachogenerator and comprises sensitivity adjustment means for varying'the relationship between the speed of movement of the driven member and that of said first control element, a second control element controlling the movement of a second movable member of said optical system, and means connecting said Isecondy control element with said sensitivity adjustment means, so that the proportional relationship between the speed of movement of the driven member and that of the first control member is dependent on the position of said second control element.

The above entitled application is continuation of U.S.

application 338,073 led Jan. 16, 1967, now abandoned.

This invention relates toa control mechanism for effecting movement of a driven member in accordance with the movement of a demand element.A Usually, although not essentially, the demand element is constituted byl al hand control movable at will by` an operator, whilst the movement of the driven member is usually but not essentially effected by means deriving its power, at least partly, from a source other than the demand element.

The object of the invention is to provide a simple and inexpensive control mechanism in which movement of the demand element produces movement of the drivenlmember with the minimum of undesirable effects due to time lag.

The control mechanism according to the invention comprises an electrically energized prime mover for driving the driven member and providing an output drive `at a speed dependent on a controlling voltage input, and a tachogenerator driven by the demand element and-having an output voltage which is approximately proportional to the speed of movement of the demand element and on which depends the controlling voltage input to the prime mover.

With this arrangement, provided that the controlling input voltage to the motor bears a constant relationship 3,400,212 ,Patented Sept. 3, 1968 ICC to the output voltage of the tachogenerator, the position of the driven member follow-s the position ofthe demand element very closely, but any error in such positional relationship is not made up after the demand elementstops since the 'prime mover also stops substantially simultaneously with such demand element. Unexpectedly, this is often advantageous.

The prime mover preferably forms part of a speed-responsive servo device wherein the controlling voltage inputis compared with a voltage dependent vonthespeed of the prime mover. For example, a preferred arrangement of such speed-responsive device comprises a reversible electric motor directly driving a second tachogenerator, one or more controlling voltage inputs to the motor beingderived from the outputs of the first and second tachogenerators.

Sensitivity adjustment means may bejprovided for varying-'the relationship between the speed of movement of the -driven member and the speed of movement of the demand element. In this case, the positional relationship between the demand element and the driven member becomes variable with operation of such means. Such means may act, for example, to vary the magnitude of the voltage input to the prime mover, such voltage input remaining also dependent on the speed of the demand element. When a speed-responsive servo-device is employed, such Isensitivity adjustment means may conveniently comprise means for varying the relative magnitudes of the voltages which are compared in the speed-responsive servo-device.

One useful application of the above-described mechanism is in the control of an optical system, wherein the driven member is constituted by an optical member movable within the system to effect focussing `and the demand element is constituted by a focussing control element.

For example, the optical system may consist of an optical objective of the zoom type having members relatively movable under the control of a zoom control element for effecting continuous variation of the equivalent focal length of the objective throughout a range whilst maintaining constant the position of the image plane, and also having part of the objective movable under the control of 'a focussing control element to suit different object distances. In such an objective, the depth of focus varies appreciably with variation in the equivalent focallength. For example, in an objective having a maximum equivalent focal length ten times that of the minimum equivalent focal length, the depth of focus at minimum equivalent focal length may be about one hundred times that at maximum equivalent focal length. This is disadvantageous in that the independent focussing control is only of appropriate sensitivity, even within fairly wide acceptable limits.

for one portion of the range of variation of equivalent focal length. For controlling such an objective of the zoom type, the movement of the zoom control element may conveniently also act progressively to va-ry a transmission ratio in the transmission between the focussing control element, and the movable 'part of the objective controlled thereby. Thus, in the present control device, the zoom control element is linked with the sensitivity adjustment means. In this connection it should be mentioned that the sensitivity adjustment means may act to vary the said transmission ratio either continuously or in steps andthe term progressively is to be interpreted accordingly. For rendering the focus control of :appropriate sensitivity throughout the range of zoom, the sensitivity adjustment means is conveniently arranged to act in such a manner that, for a given operation of the focussing control, the movement of the part of the objective movable for focussing progressively increases towards the end of the range of zoom corresponding to the smallest equivalent focal length, and vice versa.

3 v Further features of the invention will be apparent from the practical arrangements of control mechanism now-to be described by way of example with reference to the following drawings, for convenience also with reference to the use ofsuch Amechanism in controlling an optical objective of the zoom type also having a focussing control. The optical objective will be assumed to form part of a camera, for example a television camera, having the object at its front and the objective controls at its rear, with 4an adjacent monitor screen for use by the operator. In the drawings,

FIGURE 1 shows, in diagrammatic form, the television camerawith the control mechanism mounted thereon.y

FIGURES 2 to 4 respectively show details of three dif# tering preferred practical arrangements of the control mechanism of FIGURE 1, operating on an electricaldirect-current basis and each incorporating a servo-device and sensitivity adjustment means, j

FIGURE 5 shows an alternative practical arrangement of control mechanism corresponding to that of FIGURE 2 but operating on an alternating-current basis,

rFIGURE 6 shows a further practical arrangement of control mechanism wherein the servodevice is replaced by an equivalent feed-back device,

FIGURE 7 shows yet a further practical arrangement of control mechanism wherein the servo-device employs a special construction of electric motor,

FIGURES 8 and 9 show two simple arrangements of control mechanism wherein the sensitivity adjustment means is omitted,

FIGURE 10 shows an arrangement of control mechanism not employing a servo-device or equivalent feedback device, and

FIGURE ll shows the arrangement of FIGURE l0 with the inclusion of sensitivity adjustment means.

In the arrangement of FIGURE l, the focussing control element is in the form of a .hand wheel A which is coupled through gearing A1 to the input shaft B1 of a tachogenerator B to drive such tachogenerator at a considerably faster speed than the speed o-f the hand wheel. This tachogenerator B and the associated gearing may conveniently be accommodated in a small housing C on the side of the camera D at its rear end. The gearing A1 may of course be arranged in various ways other than that shown and may if desired be replaced by a friction drive.

The output of the tachogenerator B, which is proportional in sense and magnitude to the sense and speed of movement of the hand wheel, is fed to an electrical servodevce contained in a housing E on the side of the objective housing F at the front of the camera D. In FIGURE l, the sizes of the housings C and E are considerably exaggerated for clarity, since in practice these housings and the parts within them may be quite small. The servodevice comprises a reversible electric motor G and a second tachogenerator G1 having an input shaft G2 rigid with the output shaft G3 of the motor, the motor output being taken from this shaft through reduction gearing H so as to drive the part of the objective movable to effect focussing. In a preferred arrangement, the movable part of the objective is constituted by a part F2 of the front member of the front assembly of the objective only, accommodated within the enlarged front part F1 of the objective housing F, and is movable by means of a simple helical drive requiring relatively low torque, This enables a relatively low power drive to be employed, so that an electric motor of small size may be employed, together with quiet gearing.

The servo-device also includes a high gain multi-stage amplifier I (see FIGURE 2), to which is applied not only the output voltage of the first tachogenerator B driven by .the hand wheel A, but also a voltage derived from the output voltage of the second tachogenerator G1 driven by the motor G.

i I' As also shown inYFIGURE 2, the output of the second tachogenerator G1 is fed back to the amplifier I, in opposition to the input voltage due to the first tachogenerator B, through a potentiometer K which is controlled by the zoom control element (not shown). Thus, the second input voltage to the amplifier I is constituted by the output voltage of' the second tachogenerator G1 attenuated by the potentiometer K, the degree of attenuation depending on the position of the zoom control element and thus on the equivalent focal length of the objective. In FIGURE l, the gear driving the parts F3 of the objective movable within the objective housing F for zooming is shown at L, with a gear coupling L1 between this driving gear L and the potentiometer K. The gear L may be driven from the zoom control element in a variety of ways, but conveniently a servo-device may be employed for this purpose also, as will later be referred to in connection with FIGURES 8 and 9.

The operation of the above-described servo-device may best be understood by first considering focus control while the zoom control L, L1 is held fixed, whereby the attenuation aforded by the potentiometer K remains constant, so that the input to the amplifier J due to the second tachogenerator G1 is dependent only on the speed of the motor G and thus on the` speed of movement of the movable part F2 of the objective. The arrangement, in this circumstance, constitutes a speed controlling servo-device in which the speed of the driven member F2 is proportional to the speed of the hand wheel A, and the change in position of the movable part of the objective proportionately corresponds to the change in position of the hand wheel. In contrast with a position-controlling servo-device, however, there is substantially no time lag in the response of the movable part F2 of the'objective to stopping of the hand wheel A, the movable part of the objective stopping substantially simultaneously with stopping of the hand wheel. This feature, which is effective whatever the setting of the potentiometer K, is advantageous when the operator is working by use of a monitor screen. On the other hand, even with potentiometer setting constant, it will be realised that the positional relationship between the movable part F2 of the objective and the hand wheel A is less exact than in the case of a position servo-device, since any error in such relationship, for example due to saturation of the servo-device, is not made up after the hand wheel is stopped. Thus, when the hand wheel A is stopped, a large reversing voltage is at once applied to the motor G from the second tachogenerator G1, whereby the motor stops substantially immediately.

The potentiometer is driven from the zoom control element through the gearing L, L1 so that, at maximum equivalent focal length, the output voltage of the second tachogenerator Gl has maximum effect, and progressively at reduced equivalent focal lengths, increasingly less effect. The result of this is that, for a given rotation of the hand wheel A, `only a small movement of the movable part F2 of the objective occurs at maximum equivalent focal length and such movement increases progressively towards the end of the range of zoom corresponding to scale is about a hundred, but since variation in sensitivity of the focus control is acceptable within fairly wide limits, the potentiometer K will usually be arranged only partly to offset the change in depth of focus, so as to maintain such sensitivity within such acceptable limits.

The presence of the potentiometer K in the feed-back circuit of the servo-device means that there is nopredeterminable relationship between the position of the movable part F2 of the objective and the position of the hand wheel A, since Vthe movement of the hand wheel to effect focussing at any particular time is dependent on the position of the zoom control element. However, this is not disadvantageous since, when the operator is working from a monitor screen, it is usually unnecessary to provide any focussing scale for the hand wheel. Nevertheless, it should be made clear that, apart from the other advantagesthereof, it is the use of aspeed-controlling servo-device, rather than a position-controlling servo-device, which makes practicable the use of the above-described potentiometer K for sensitivity adjustment. With a position-controlling servo-device, it is impracticable to effect sensitivity adjustmentby means 'of such a potentiometer, without causing undesired movement of the movable part F2 of the objective. It is to be noted that, in the above-described arrangement, movement of the zoom control element does not affect the focus setting, which is adjusted solely by movement of the focussing control hand wheel A.

It will be clear that the above-described potentiometer K may alternatively be used tovary the proportion of the input voltage of the first tachogenerator Bwhich is applied to the amplifier J, as shown in FIGURE 3, or yet again be used as a potential divider acting to vary the attenuation in inverse proportions, of the output voltages of both tachogenerators B and G1, as shown in FIGURE 4. It is also practical to incorporate suchv potentiometer as part of a push-pull circuitV in the amplifier. Furthermore, such potentiometer K may be replaced by a variable reactance device in an alternating-current system. By Way of example, FIGURE 5 illustrates an alternating-current system generally analogous to the arrangement of FIG- URE 2. Control windings for the tachogenerators B and G1'and the motor G are shown at B2, G'I and B8 respectively, connected across a common alternating-current source. The arrangements of FIGURES 3 to 5 will be clear without further descrip-tion, and in these figures the same reference letters are used as in FIGURE 2 for corresponding parts. In each of FIGURES 2 and 5 and in further figures, the broken line G4 serves to indicate that the output shaft G3 of the motor G is rigid with the input shaft G2 of the tachogenerator G1.

In an alternative arrangement of control device operating on a direct-current basis and shown in FIGURE 6,` the above-described servo-device is replaced by an analogous device comprising a reversible direct-current electric motor G, connected in one arm of a bridge circuit also comprising resistances M and a compensating inductance for the motor M1. An amplifier J1 has two inputs, respectively positive and negative, to which are applied positive and negative outputs from the first tachogenerator B and negative and positive feed-backs from two opposite corners ofthe bridge circuitG, M and M1. The output of the amplifier I1 is taken to a third corner of the -bridge circuit, the fourthcorner being earthed. With this arrangement, the feed-back'to the amplifier .I1 is representative of the back electro-motive-for'ce of the motor G, which is dependent on the speed thereof. A potentiometer for sensitivity 'adjustment may be incorporated either in the feed-back circuitsor in the output circuits of the first tachogenerator or in the amplifier. Alternatively, as indicated by the broken lines, such potentiometer, which is formed in two ganged parts K1, in view of the two inputs to the amplifier J 1, may act as a potential divider between the output voltage of the first tachogenerator B and the feed-back voltage of the bridge circuit G, M and M1. With this arrangement, the voltage applied to the motor, for a fixed position of the potentiometer K1, K2, is as before proportional to the difference between two voltages proportional to the speeds of the focussing control hand wheel A and the movable part F2 of the objective, so that the arrangement in effect constitutes a speed-controlling device acting in the same manner as the servo-device in the arrangement previously described.

The arranvement last described with reference to FIG- URE 6` is illustrative of a number of ways in which a feed-back circuit may be employed to cause a correcting voltageto be applied to the motor G, without requiring the use of a second tachogenerator.'Moreover, if desired, instead of a single controlling input voltage for the motor, derived from the output voltage of the first tachogenerator and from the feed-back voltage, the last two mentioned voltages may be amplified and used""to provide two controlling input currents for a motor, for example of the constant armature current type, having two control field windings. In this instance, which is illustrated in FIG- URE 7, the two currents are amplified by means of a two part amplifier J2, I3 and are compared in the motor, indicated at G5, and a correcting torque is applied at the output shaft G3. In this arrangement, as in other arrangements, the potentiometer constituting the sensitivity adjustment means may be connected in the circuit of either controlling input voltage, for examplel as indicated at K in the output circuit vof the tachogenerator B. While the arrangement of FIGURE 7 shows a control mechanism also incorporating a second tachogenerator G1 so as to form a servo-device, a constant armature current motor with two field windings may alsoibe vemployed to compare the tachogenerator output voltage and the feedback voltage in an arrangement generally similar to that shown in FIGURE 6.

The above -described arrangements of control device, incorpo-rating sensitivity adjustment means, may be used for purposes other than controlling an optical objective of the zoom type. For example, such arrangements may be applied to the control of an adjustable gun turret, wherein the sensitivity of the azimuth drive transmission is determined by the setting yof the elevation control. Yet again, these arrangements may be applied to controlling an optical system with a movable focussing element and an adjustable iris diaphragm, adjustment of which causes changes in the depth of focus afforded by t-he system. In this instance, the transmission to the focussing element incorporates the sensitivity adjustment means, which is linked to the iris diaphragm control.

Furthermore, the present invention is in no way limited to the provision of sensitivity adjustment means, but may be employed in any instance where it is desired to move a driven member in response to movement of a demand element with the minimum of undesirable effects due to time ilag, the exact positional relationship between the driven member :and the demand element being of subsidiary importance. For example, in an optical system having a lens or other optical element movable for focussing purposes, the operator is invariably provided with a screen or other means whereby the effect of adjustment `of the focus control is rendered visible, so that 4accurate -focus adjustment is most readily facilitated if the movable focussing element is stopped substantially simultaneously with the stopping of the focussing demand element. This is achieved by the speed-controlling means utilised in the present invention, which enables the operator to move the demand element until the desired result, for exam-ple exact focussing, is obtained, regardless of the precise positional change of the demand element which is required to bring about such result.

Thus, for completion of the understanding of the invention, FIGURES 8 and 9 show two arrangements which are respectively similar to the arrangements of FIGURES 3 and 4 except that the sensitivity adjustment means is omitted. In these figures, the same reference letters as those employed in previous figures are retained for similar parts. Either of these lmodified arrangements may conveniently be employed for driving the gear L for moving the parts F3 -of the objective movable to effect zooming, the tachogenerator B being driven from the zoom control element.

FIGURE 10 shows a very simple arrangement of the invention which may be useful in certain applications, more especially when the velocity, at which the velocity demand element is to be moved, lies within a relatively limited velocity range. Thus, in this simple arrangement, a

servo-device is not employed, but the output of the rst tachogenerator B is fed through an amplifier I directly to a motor G6 as the sole controlling voltage therefor, such motor conveniently being of the well-known kind whose speed is proportional to its input voltage throughouta chosen range. Finally, FIGURE 11 shows a modification of the arrangement of FIGURE wherein sensitivity adjustment means K is incorporated in the output circuit of the tachogenerator B.

What I claim as my invention and desire to secure by Letters Patent is:

41. In an optical system comprising an optical objective of the zoom type wherein zooming is controlled by a zoom control element, a control mechanism for effecting movement of an optical member movable for focussing in accordance with the movement of a focussing control element, comprising an electrically energized prime mover for driving the movable member of the objective and having an output drive whose speed is dependent on a controlling voltage input to such prime mover, a tachogenerator having an output voltage approximately proportional to the speed, at which it is driven, a transmission mechanism interposed between the focussing control element and such tachogenerator whereby the tacho generator is driven at a speed greater than and approximately proportional to the speed of movement of the focussing control element, amplifying means whose output constitutes the said controlling voltage input to the prime mover, circuit means whereby the input to the amplifying means is dependent on the output voltage of the tachogenerator, sensitivity adjustment means in said circuit for varying the relationship between the speed of movement of the driven member and the speed of movement of the focussing control element, and means connecting the zoom control element with the sensitivity adjustment means in such a manner that corresponding operations of the focussing control at the two end portions of the range of variation of equivalent focal length respectively result in greater and lesser movements of the part of the objective movable for focussing.

2. A control mechanism as claimed in claim 1 in which the sensitivity adjustment means acts in such a manner that, for a given operation of the focussing control, the movement of the part of the objective movable for focussing progressively increases towards the end of the range of zoom corresponding to the smallest equivalent focal length, and vice versa.

3. A control mechanism for an optical objective of the zoom type for effecting movement of an optical member movable for focussing in accordance with the movement of a focussing control element, comprising an electrically energized prime mover for driving the movable part of the objective and having :an output drive whose speed is dependent on a controlling voltage input to such prime mover, two tachogenerators each having an output voltage approximately proportional to the speed at which it is driven, means whereby the first tachogenerator is driven at a speed approximately proportional to the speed of movement of the focussing control element, means whereby the second tachogenerator is driven by the prime mover, circuit means whereby the controlling voltage input to the prime mover is dependent upon the output voltages of the two tachogenerators, a zoom control element for controlling zooming of the objective, and sensitivity adjustment means operatively connected to the zoom control element for varying the relationship between the speed of movement of the driven member of the objective and the speed of movement of the focussing control element in accordance with movement of the zoom control element.

4. In a optical system, a control mechanism for effecting movement of a movable optical member of said system in `accordance with the movement of a first control element, said mechanism comprising an electrically energized prime mover for driving said movable member and having an output drive whose speed is dependent on a controlling voltage input to such prime mover, a tachogenerator having an output voltage approximately proportional to the speed -at which it is driven, a transmission mechanism interposed between said first control element and such tachogenerator whereby the tachogenerator is driven at a Speed greater than Iand approximately proportional to the speed of movement of said rst control element, amplifying means whose output constitutes the said controlling voltage input to the prime mover, means for supplying an input to the amplifying means which is dependent on the output voltage of the tachogenerator and comprises sensitivity Iadjustment means for varying the `relationship between the speed of movement of the driven member and that of said first control element, a second control element controlling the movement of a second movable member of said optical system, and means connecting said second control element with said sensitivity adjustment means, so that the proportional relationship between the speed of movement of the driven member and that of the first control member is dependent on the position of said second control element.

References Cited UNITED STATES PATENTS 2,147,674 2/1939 Satterlee 318--30 2,443,048 6/1948 McComb 95-45 2,891,206 6/1959 Dillonaire 318--327 2,720,817 10/1955 Mills 88-57 2,782,683 `2/1957 Walker 88-57 2,984,154 5/1961 Walker 88-57 3,093,784 6/1963 Mintzer 318-327 3,283,231 ll/l966 Askew 318-30 ROBERT L. GRIFFIN, Primary Examiner.

I. A. ORSINO, Assistant Examiner. 

